Top Circuits Page 9
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The JFETs, Ql and Q2, provide complete buffering to Cl, the sample and hold capacitor. During sample, Ql is turned on and provides a path, rds(on), for charging Cl. During hold, Ql is turned off, thus leaving Ql Id (< 100 pA) and Q2 Igss (< 100 pA) as the....
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This circuit exhibits a 10 V acquisition time of 900 ns to 0% accuracy and a droop rate of only 100 µ-V/ms at 25° C ambient condition. An even faster acquisition time can be obtained using a smaller value hold-capacitor. By decreasing the value from 1000....
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The circuit charges and discharges a capacitor at a crystal-controlled rate, and stores on a sample-anddifference amplifier the change in voltage achieved. The current that flows during the discharge cycle is averaged, and ratiometrically measured in the....
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U1a is an oscillator and U1b tbe measurement part of tbe circuit. It converts unknown capacity into a pulse-width modulated signal the same way an·automotive dwell meter works. The meteris linear so tbe fraction or percentage of time that tbe output is....
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The two-pole, five-position switch, coils and 365-pF variable capacitor cover a range from 1.5 to 30 MHz. The amplifier uses Darlington npn transistors whose high beta, 5000, provides high sensitivity with Sl used as the amplifier on/off switch. Switch S2....
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The untuned, but amplified FSM can almost sense that mythical flea"s whisper-from 3 through 148 MHz no less-and yet, is so immune to overload that the meter pointer won"t pin. The key to the circuit is the amplifier, a 324 quad op amp, of which only one....
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The circuit monitors and displays a digital signal"s duty cycle and provides accuracy as high as ±1%. Using switch S2, you can choose a frequency range of either 250 Hz to 2. 5 kHz at ±1% accuracy or 2 kHz to 50 kHz at ±10% accuracy. The common-cathode....
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This circuit is designed around a 4049 hex inverter/buffer. Two inverters are used ina dual-frequency signal-injector circuit, another inverter is used as a logic probe, and the remaining three inverters are used as a sensitive dual-input, audio-signal....
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The Hewlett-Packard HSCH-3486 zero-bias Schottky diode is used as the detector. To avoid using a modulation method of detection, a chopperstabilized op amp is used. The chopper op amp basically converts the input de voltage to ac, amplifies it, and....
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The circuit is based on the grid-dip or absorption effect, which occurs when a parallel resonant circuit is coupled to an oscillator of tbe same frequency. Ql operates in a conventional Colpitts oscillator circuit at a fixed frequency of approximately 4....
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In machine and equipment design. some applications require measurement of both the shaft speed and the direction of rotation. Fig. 56-4 shows the circuit of a tachometer, which also indicates the direction of rotation. The flywheel has two magnets embedded....
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This circuit operates by charging a small capacitor from a constant-current source when the pulse to be measured is present. Dual pnp transistor Q3 is the current source; its output current equals the LM329 reference voltage divided by the resistance of....
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The design shown is a simple unit for QRP operation on all authorized frequencies up to 30 MHz. based on a toroidal transformer Tl. The secondary winding of Tl samples a small amount o1 rf power. both forward and reflected, which is divided by the bridge....
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The circuit in Fig. 56-lla lights the signal lamp upon detecting a line current consumption of more than 5 mA, and handles currents of several amperes with appropriate diodes fitted in the D1 and D2 positions. Transistor T1 is switched on when the drop....
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The circuit outputs power to the drive motor when one or no sheets are being fed, but interrupts motor power when two or more superimposed sheets pass through the optodetector slot. The optodetector can be either an H2aB darlington interruptor module or an....
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The CS209 is designed to detect the presence or proximity ofmagnetic metals. It has an internal oscillator that, along with its external lc resonant circuit, provides oscillations whose amplitude is dependent upon the Q of the lc network. Close proximity to....
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In this application, the ICM7249 is configured as an hours-in-use meter and shows how many whole hours of line voltage have been applied. The 20-MD resistor and high-pass filtering allow ac line activation of the SIS input. This configuration, which is....
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A transducer senses a direct current magnetically, providing isolation between the input and the output. The detecting-and-isolating element is a saturable reactor, in which the input current, to be measured, passes through a one-tum control coil. The....
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This design is for an external signal strength meter that is analog, digital, and audible for mobile transmitter hunters. The S meter also incorporates a gain circuit. The digital LED bar graph display has a very fast response time. The 3.3-KO resistor....
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Remote, noncontact, measurement of the speed of rotating objects is the purpose of this simple circuit. Linearity and accuracy are extremely high and normally limited by the milliammeter used and the initial calibration. This circuit is configured to count....
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The adapter allows four inputs to be displayed simultaoeously on a single trace scope. For low-frequency signals, less than 500Hz, the adapter is used in the chop mode at a frequency of 50 kHz. The clock can be run faster, but switching glitches and the....
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This circuit turns a common oscilloscope into a versatile eight-channel display for direct voltages. The trend of each of the eight input levels is readily observed, albeit that the attainable resolution is not very high. The circuit diagram shows the use....
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The calibrator can be used to check the accuracy of a time-base generator, as well as to calibrate the input level of amplifiers. The calibrator consists of an NE555 connected in the astable mode. The oscillator is set to exactly 1 kHz by adjusting....
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This circuit provides 20 ±0.1 dB voltage gain from 0. 5 to 25 MHz and ± 3 dB from 70 kHz to 55 MHz. An LM733 video amplifier furnishes a low input-noise spec, 10-I"V typical, measured over a 15.7-MHz bandwidth. ..
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The operation of the unit revolves around three !Cs: a 4093 quad NAND Schmitt trigger, a 4066 quad analog switch, and a 7555 timer. When a high is fed to probe 1 in, it is inverted to IC1a and once again by IC1b, so that the input to IC2a is high. Thathigh....
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This circuit provides about 20 dB voltage gain with a frequency range from 0.5 to 50 MHz. You can extend tbe low-frequency response of this circuit by increasing tbe value of the 0.05-ILF capacitor- or try removing tbe capacitor. This circuit delivers a....
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The circuit will provide a 20 ±0.1 dB voltage gain from 500 kHz to 50 MHz. The low-frequency response of the amplifier can be extended by increasing the value of the 0.05-JLF capacitor connected in series with the input terminal. This circuit will yield....
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The circuit"s input op amp triggers the timer, sets its flip-flop and cuts off its discharge transistor so that capacitor C can charge. When capacitor voltage reaches the timer"s control voltage of 0.33 Vee. the flip-flop resets and the transistor....
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IC1a, IC1b, and IC1c of the quad two-input NAND gate 4011 are connected as an astable multivibrator; IC1d is connected as an inverter. Terminals 3 and 11 of the 4011 produce square waves with opposite phases. The square waves, eP, at the output of IC1a,....
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Two important properties of the 8043 are used to advantage in this circuit. The low input bias currents give rise to slow output decay rates (droop) in the hold mode, while the high slew rate at 6 V/p,s improves the tracking speed and the response time of....
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Feedback is the same as a conventional op-amp voltage follower which yields 11 unity-gain, noninverting output. This hookup also has a very high input impedance. The only difference between a track-and-hold and a sample-and-hold is the time period....
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This circuit uses the speed and drive capability of the HA-5190 coupled with two high-speed DMOS FET switches. The input amplifier is allowed to operate at a gain of -5, although the overall circuit gain is unity. ..
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Itis often required that a signal be filtered prior to sampling. This can be accomplished with only one device. Use any of the inverting and noninverting filters that can be built with op amps. ..
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The sample-and-hold function has often been accomplished with separate analog switches and op amps. These designs always involve performance tradeoffs between acquisition time, charge injection, and droop rate. The HA-242-/2425 monolithic....
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The LM101A provides gain and buffers the input from storage capacitor C2. R2 adds a zero in the open loop response to compensate for the pole caused by the switch resistance and C2, improving the closed-loop stability. R1 provides a slight delay in the....
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Channel 1 is wired as a voltage follower and is turned on during the track/sample time. Ifthe product of R x Cis sufficiently short compared to the period of maximum output frequency, or sample time; Cwill charge to the output level. ..
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This illustrates another application in which the hookup versatility of a sample-and-hold often elimi nates the need for a separate op amp and a sampleand- hold module. ..
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This tachometer lets you measure heartbeats, respiratory rates, and other low-frequency events that recur at intervals of 0.33 to 40.96 seconds. The circuit senses the period offm, computes the equivalent pulses per minute, and updates the LCD accordingly.....
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A standard shaft encoder"s A and B ports generate square waves with the same frequency as the shaft turns. The phase of A will lead or lag that of B by 90°, ~depending on the direction of rotation. To obtain maximum resolution, the tachometer circuit must....
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If the tube is level with respect to gravity, the bubble resides in the tube"s center and the electrode resistances to common are identical. As the tube shifts away from level, the resistances increase and decrease proportionally. Transducers of this type....
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The 5-MHz track and hold shown here has a 400-kHz power bandwidth driving ±10 V. A buffered input follower drives the hold capacitor, C4, through Ql, a low resistance FET switch. The positive hold conuuand is supplied by TTL logic, with Q3Ievel shifting....
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When the switch is closed or the FET is conducting, the circuit behaves as an inverting amplifier with a gain of R2/Rl. Since as the inverting tenninal of the op amp is a virtual ground, the capacitor is kept charged to the output voltage by the op amp.....
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This circuit reads and stores voltages, tbus freezing the meter reading even after tbe probes are removed. The op amp is configured as a unitygain voltage follower, witb C1 situated at tbe input to store tbe voltage. For better performance, use an....
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In a single difference amplifier configuration, the AM-427 exhibits excellent common-mode rejection and spot nois..
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An Intersil 7101 31/2-digit A/D converter is used to display the duty cycle of a pulse train as a percentage. The frequ..
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This simple adapter uses an oscillator (567) to drive a counter (U2) and switch (U3) that selects the outpu..
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This system can be used with 4-, 6-, or 8-cylinder automobiles. The timebase formed by IC5 is an oscillator th..
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This circuit develops an output voltage that is proportional to the magnetic induction, B, flowing through its probe"s coi..
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When an input voltage is positive, the output of ICA is negative and diode D does not conduct; hence the outp..
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This circuit measures capacitance by the time it takes an unknown capacitor to reach 6.32 V (10 V 63% or 1RC time const..
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Sometimes electrolytic capacitors that are stored for some time will exhibit high leakage currents..
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The equivalent series resistance (ESR) of a capacitor can be measured using this circuit and an ac voltmeter. Ul fun..
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The circuit uses a synchronous-detection scheme to measure low-level resistances. Other low-resis-tance-measuring circui..
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This continuity checker (built around an LM339 quad comparator with open-collector outputs) eliminates false r..
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A continuity tester that has an audible indicator can be more useful in some cases than a visual indicator, because you n..
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For checking resonances, tuned circuits, antennas, etc., this circuit covers the 2-to 20-MHz range. Ql serves a..
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Ll and L2 form a tuned transformer. About a 1:3 turns ratio is optimum. L2 and CI tune to the desired frequency. The fre..
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This field strength meter consists of a tuned crystal detector producing a dc output voltage from a transmitted signal. The dc voltage is used to shift the frequency of a transmitter of 100-mW power operating at 1650 kHz. The frequency shift is proportional....
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This circuit uses a FET as a dc amplifier in a bridge circuit. R4 is set for meter null with J1 short circuited. Any surplus 50-mA meter can serve in this circuit. RFC1 is any suitable RF choke for the band in use. A 2.5-mH RF choke will do for broadband....
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The ECM circuit consists of four sections, as shown in the block diagram. A power converter generates a voltage that is proportional to the true of real power consumed by the load. That voltage feeds both a bargraph and a voltage-to-pulse converter. The....
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The circuit includes a low-distortion, 1-kHz oscillator and will measure THD at a user selected voltage level for voltage amplifiers, or for checking amplifiers of power levels to 600 W. It will detect THD levels of .005% (-86 dB). A built-in one-percent....
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A pressure sensor (IC4) is used with a dc: amplifier to convert the bridge output (IC4) to a single-ended voltage. ICld provides a reference voltage for setting barometric pressure. IC3 is an A/D converter manufactured by Intersil. This drives an LCD....
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An electronic scale using a pressure transducer (load cell) and an analog-digital (A/D) converter to drive a digital display is shown. The scale range depends on load cell. Display is calibrated in appropriate units. Components are on main circuit and....
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This circuit is basically a system that generates a pulsed modulation signal for a Gunn diode microwave oscillator. Several speed settings are preset (S3 a and b). A 555 timer is used with a frequency divider chain to produce Doppler shift equivalents of....
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Useful for checking diodes, transistors, triacs, SCRs, resistors, and LEDs, this curve tracer should prove useful in the experimenter`s lab. It displays the volt-ampere characteristic of a two-ter-minal device on an oscilloscope. This is a simple block....
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The outputs from the comparators will swing, in sequence, from high to low as the input voltage rises above the reference voltage applied to each comparator. The output LEDs will then switch on in sequence as the voltage rises. The inverting inputs of the....
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The load`s power factor, which is the cosine of the phase angle between the voltage across the load current, can be calculated simply with this circuit. A1:1 isolation transformer is used to prevent direct contact with the line. By properly adjusting Rr,....
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Video-signal amplitude can be measured with this simple circuit, which is basically a modified standard peak detector. The device can verify RGB generated by video RAMDACs. Ul is a high-speed buffer and U2 is a latched comparator. CI is a hold capacitor.....
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Because many amateur receivers are fitted with an S meter that functions far from logarithmically, the proposed circuit should be a welcome extension of such receivers. Although ICs such as the CA3089 or the CA3189 are not in common use anymore, they serve....
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The circuit useful for distortion measurements notches out the fundamental frequency of 1 kHz to allow measurement of the residual level of harmonics. First a true RMS meter is used to measure the 1-kHz input level E^ by setting SA to the input position.....
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The unknown resistance is put in series with a known standard and a current passed through the pair. The voltage developed across the unknown is applied to the input and the voltage across the known resistor applied to the reference input..
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Suitable for monitoring an amateur band or a segment of the radio spectrum, this simple adaptor uses an NE602 mixer-oscillator chip to produce a 455-kHz IF signal, which U2 amplifies, then feeds to detector D2 and the Y axis of an oscilloscope. VT is used....
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This circuit is representative of the many applications of up/down counting in monitoring dimensional position. In the tape recorder application, the LOAD REGISTER, EQUAL, and ZERO outputs are used to control the recorder. To make the recorder stop at a....
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One can transform an ordinary binary counter, such as a 7493, into an up/down counter with mode control by adding XOR gates 7486 to the counter"s outputs. The circuit counts up when the DN/UP line is low and down when the DN/UP line is high. To use the....
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This circuit symmetrically divides an input by virtually any odd number. The circuit contains n + 1h clocks tw..
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This circuit produces a symmetrical waveform when dividing by either 2 or 3. The Divide Select input controls the ..
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This circuit, instead of dividing by an integer, divides the input signal by +1/2. With the feedback connections ..
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This circuit is used to record telephone conversations on your landline telephone. All you will need is this small circuit and subscription of your PC. There are few times when we forget what we said or told us. So we need recording. Sometime, not many years....
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Two integrated tone decoders, XR-567 units, can be connected (as shown in Fig. 1A) to permit decoding of simultaneous or sequential tones. Both units must be on before an output is given. R1C1 and R'IC'l are chosen, respectively, for Tones 1 and 2. If....
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The on-hook (no load) voltage across the red-green wires will be 48 V or slightly less when all telephones are on-hook (disconnected). When any telephone goes off-hook the load current flowing in the telephone causes the voltage to fall below 5 volts dc.....
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This circuit converts a tape recorder into a completely automatic telephone conversation recording instrument that needs no external power source. Voltage at the switch terminals of tape recorder applied to a pair of Darlington-connected transistors, Ql and....
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Transistor Ql of the headset amplifier circuit amplifies the 30 mV signal, that would have gone to the earphones, to .5 V. which sufficiently drives the stereo earphones. Capacitor Cl blocks any de current from shorting back into the telephone base.....
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This circuit shows the TP5700 directly interfacing to a low-voltage DTMF generator. VREGt supplies the necessary 2-V minimum bias to enable the TP5380 to sense key closures and pull its mute output high. VREGt then switches to a 3-V regulated output to....
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This circuit consists of two audio channels, a control circuit, and a hybrid irlterface circuit. The gain of each audio channel is con· trolled by the control circuitry, with the use of a voltage controlled amplifier (VCA). The inputs to the control....
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Here is a simple method of series connection into the telephone set suitable for PABX or short line applications. When the telephone handset is lifted, Cl is charged via D1 to (Vz1 -0.7) V and DF320 power on reset occurs. When the first keyed digit is....
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The oscillator is a Motorola MC14410CP chip using a 1-MHz crystal. The chip generates both the high and low tones, feeding the energy to the amplifier through 1-K resistors and the 1-I"F capacitor. Values for the output resistors can vary from a few....
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The TP5700 or TP5710 can reduce the number of components required to build a pulse-dialing telephone, as shown. The usual current source can be eliminated by using the VREGl output to power a TP50982A low-voltage (1. 7 V) pulse dialer via a blocking diode.....
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When the handset is lifted and power is applied to the circuit, Q2 is fed base current through R2, which in turn drives Ql. C2 is charged via R3 in series with D1 to (Vz1 -0. 7) V. When the minimum operating Vnv voltage is reached, power on reset occurs....
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A sensitive-gate SCR provides a line-holding current of 20 to 40 mA, depending on loop resistance. It also lights an LED to give the user a positive indication that the telephone line is on hold. The 20 to 40 mA should prove sufficient to hold the majority....
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This encoder uses a single contact per key keyboard and provides all other switching functions electronically. The diode connected between terminals 8 and 15 prevents the output from goitrg more than 1 V negative with respect to the negative supply Vss.....
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This indicator senses the switching on and off of the 48-V de line voltage and transmits the pulses to logic circuitry. An Hl1A10 threshold coupler, with capacitorfiltering, gives a simple circuit which can provide dial pulse indication, and yet reject....
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The telephone-line decibel meter and line-voltage sensor shown lets you accurately monitor and adjust telephone sound levels. The 600-0 resistor properly terminates the line. ..
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This circuit can be used in telephone lines for speech activity detection purposes. This detection is very useful in the case of half-duplex conversation between two stations-in the case of siroultaneous transmission of voice and data over the same pair of....
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This circuit is a bidirectional amplifier that can amplify both signals of a duplex telephone conversation. It uses the principle of negative resistance. Obviously, such an amplifier could easily be unstable; however, you can adjust Rl for maximum....
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This recorder can be connected to the telephone lines just about any place, and no external power source is needed. The tape recorder"s switch terminals are applied to a pair of transistors, connected as Darlingtons, that are used to turn the recorder on....
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Each and every time a phone on the same line or calling numberis taken off-hook, the circuit will be activated to control an external electronic circuit. If several extension telephones are used on one phone line, the circuit can be useful as a busy....
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Q1 and Q2 are used to form the basis of an interface circuit for attaching a cassette recorder to the phone line. The circuit does not require a power supply because operating power is drawn from the telephone line itself. The incoming signal is fed across....
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The IR transmitter connects to a telephone cir cuit, and transmits both sides of all telephone conversations to any line-of"sight location, within 40 feet. No !fOWer is taken from the central office, as long as all phones remain on-hook. The current....
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Audio from the telephone is inductively coupled to the base of Ql. which is used as a preamp. The preamp provides a gain of about 75 dB, to boost the input signal from .about 4 mV to about 300 mV pk-pk. If you use a higher gain transistor, increase the....
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Amplify or record a telephone call with the simple circuit shown. The 8-0 secondary winding of a miniature transistor output transformer is connected in series with either of the telephone lines. ..